A typical electrochromic (EC) device is categorized into a solid-type or a liquid-type. The structure of the solid-type EC device is formed on a transparent substrate, and a plurality of coating layers (e.g., a transparent conductive layer, an EC thin film, a solid electrolyte, and an ion storage layer) having different functions are successively vacuum deposited on the substrate. By contrast, the structure of the liquid-type EC device is formed by two conductive transparent substrates, wherein EC coating layer, ion storage layer, and an electrolyte solution are disposed between the two conductive transparent substrates.
Compared to electrochromic device which has been developed for some time, the integration of photovoltaic (PV) and electrochromic (EC) provides better efficiency in saving energy, for the photovoltaic electrochromic (PV-EC) device can achieve color change in EC layers without additional power supply. Researches that integrate photovoltaic technology have provided diverse application of electrochromic device, for instance, building integrated photovoltaic (BIPV) may be cooperated with the electrochromic technology to automatically adjust the colors of electrochromic windows to reduce indoor heat.
There are two types of solar powered EC devices, dye-sensitized solar cell (DSSC) and silicon based PV-EC device. The DSSC-EC technology separates the photoabsorbing layer-TiO2 and the EC layer to the anode and the cathode respectively for constituting a device. At the beginning, this technology is developed based on the concept of using compound films of a Prussian blue electrochromic thin film and a photosensitive layer-TiO2 for performing color change. In recent years, such a concept has been further extended to separate the photosensitive layer and the electrochromic layer to the anode and the cathode respectively for constituting a device. This device can be described as having EC materials inserted into DSSC which has become the most widely-discussed topic in the research of the integration of photovoltaic and electrochromic technology. However, to apply such a structure to practical applications, many problems need to be overcome, such as the long term stability of the photosensitive layer or the feasibility of developing devices having large dimensions.
Another research is a stand alone side-by-side integration of a silicon thin film solar cell with an EC device, an appropriate switches are employed to control the EC device and the thin film solar cell, as was disclosed in U.S. Pat. No. 5,384,653. A control box disclosed in this patent switches the colored/bleached state of the EC device through the solar cell or a battery.
Moreover, U.S. Pat. No. 5,377,037 disclosed a design of monolithic integration of a silicon thin film solar cell and an EC device on one single substrate. Specifically, a silicon thin film solar cell and an inorganic EC device are combined on a first conductive glass substrate by conducting a tandem approach, then another transparent conductive glass substrate is disposed on the opposite side facing the thin film solar cell. A liquid organic electrolyte solution or a solid inorganic electrolyte layer is disposed between the two substrates. In said device, a preset bleed resistor is applied to accomplish a switch control of the EC material, and the bleed resistor connects the EC material and the thin film solar cell.